Many people die yearly from sudden cardiac death. In the vast majority of these cases, the cause of death is ventricular tachycardia and/or ventricular fibrillation. Automatic implantable cardioverting/defibrillating devices have been developed and shown to be effective in preventing sudden cardiac death from these causes.
Cardioversion (performed by a cardioverter) may be defined as the correction of either ventricular tachycardia or ventricular fibrillation by the discharge of electrical energy (e.g., shock) into the heart. The shock may be either synchronized or non-synchronized. Ventricular tachycardia is an abnormally rapid heart rate (120-240 beats per minute) originating in the heart""s main pumping chambers (ventricles) which is regular in periodicity and often is life threatening to the patient. Ventricular fibrillation is generally a more rapid heartbeat disorder, disorganized and irregular, or non-periodic, and is often fatal unless corrected within minutes by the discharge of electrical energy through the heart. Sometimes, cardioversion may include delivery of an electric shock to the heart to correct ventricular tachycardia. Defibrillation may likewise include the non-synchronized delivery of electrical energy to the heart to correct ventricular fibrillation.
A plurality of different types of implantable cardioverter defibrillation (ICD) systems are known in the art. For example, see each of U.S. Pat. Nos. 4,030,509; 4,662,377; 5,133,365; and 6,067,471; the disclosures of which are all hereby incorporated herein by reference. ICD systems may be used to provide electric shock to the heart in order to correct ventricular fibrillation. FIG. 1 illustrates an internal lead 3 of a conventional ICD system placed in the right ventricle 5 of a patient""s heart 4. The distal tip electrode 6 is located in the right ventricular apex 7. Labeled boxes in the figure illustrate the directions in which blood is pumped throughout the body by the heart. Additional details of the FIG. 1 system are described in the aforesaid ""365 patent.
Unfortunately, use of ICD systems may often be painful to the patient to which the shock is applied. A reason for this is that defibrillation shocks often extend beyond the heart and activate extracardiac muscle(s) and/or nerve tissue(s) within the peripheral chest area(s). Excessive pain is not desirable.
It will thus be apparent to those skilled in the art that there exist a need for an ICD system and/or method that may be less painful to a patient than one or more conventional ICD systems and/or methods.
An object of this invention is to provide an implantable cardioverter defibrillator (ICD) system and/or method that is less painful to a patient than one or more conventional ICD systems/methods.
Another object of this invention is to provide a flexible array including a plurality of electrodes for surrounding at least a portion of the heart, for use in an ICD system/method. In certain embodiments, individual electrodes in the array are selectively coupled to one another so that the electrodes may be electrically floating relative to one another during certain modes of ICD operation (e.g., heart monitoring modes) and electrically coupled to one another in other modes of ICD operation (e.g., shock modes).
Another object of this invention is to utilize the flexible array described above in a manner such that when the individual electrodes are electrically coupled to one another, a type of Faraday cage (e.g., xe2x80x9cquasi-Faraday cagexe2x80x9d) is formed around a portion of the heart. This quasi-Faraday cage at least partially (or even fully in certain embodiments) confines the defibrillation shock field to the heart itself so that the shock does not activate extracardiac muscle(s) and/or nerve tissue(s) in the surrounding chest. This enables the ICD system and/or method to be less painful than one or more certain conventional ICD systems/methods.
Another object of this invention is to provide a selectively activatable Faraday cage, or quasi-Faraday cage, for use in ICD systems, or any other type of system including but not limited to non-medical applications.
Yet another object of this invention is to fulfill one or more of the aforesaid needs and/or objects.
In certain embodiments of this invention, an ICD system includes an internal electrode placed in the right ventricle of the heart, and a flexible array (that includes a plurality of electrodes) placed over a significant portion of the heart. Defibrillation shocks are applied between the internal electrode in the ventricle and the electrodes in the flexible array. Because the electrodes in the flexible array surround a significant portion of the heart, the array functions as a quasi-Faraday cage and thus is capable of confining a significant portion of the defibrillation shock field to the heart itself. As a result, defibrillation shocks do not activate extracardiac muscle(s) and/or nerve tissue(s) within the surrounding chest. Thus, application of the shocks is less painful.